[en] The present work tries to solve the problem of realizing a parametric conceptual CAD model of a modular reactor for future inertial fusion power plants. The choice of a modular structure seems to be a good solution for efficiency and economic requirements. On the other hand, the realization of a parametric-variational CAD model is very useful to optimize nuclear and mechanical parameters and to permit the shift from the conceptual to the final model. First, geometric solutions for a modular reactor are analysed; the most interesting is that of a 20-face regular polyhedron (icosahedron). The subdivision of each face into six equal triangles consents to obtain a mono-modular reactor with 120 modules (called 'ICO120'). This solution should be easy, efficient and cheap. Secondly, the work proposes a conceptual CAD model of the ICO120 reactor in which special attention is put on the parametrization. Starting from such parametric model it will be possible to develop and optimize icosahedral reactors with different features, sizes and performances